Winger Chris Taylor has agreed personal terms and passed a medical at Millwall.
Taylor, who was out of contract at League One side Oldham, will officially sign a one-year deal with the Lions on June 15.
Millwall manager Kenny Jackett told the club's website: "Chris has played a lot of games at League One level and is ready to make the step up to the Championship.
"Hopefully he will enjoy a fresh start and give us a real option down the left side."
Taylor added: "I'm really looking forward to joining Millwall.
"After spending all my career at Oldham I had to give my next move a bit of thought, but I know that this is the right one and I can't wait to get started."